header-background.hbs

 .responsive-header-img {
      background-image: url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_2000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="xl"absolute="true"}});
  }

  @media(max-width: 1000px) {
      .responsive-header-img {
          background-image: url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_1000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="l" absolute="true"}});
          background-image: -webkit-image-set(url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_1000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="l" absolute="true"}}) 1x,
              url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_2000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="xl" absolute="true"}}) 2x);
          background-image: image-set(url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_1000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="l" absolute="true"}}) 1x,
              url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_2000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="xl" absolute="true"}}) 2x);
      }
  }

  @media(max-width: 600px) {
      .responsive-header-img {
          background-image: url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_600,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="m" absolute="true"}});
          background-image: -webkit-image-set(url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_600,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="m" absolute="true"}}) 1x,
              url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_1000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="l" absolute="true"}}) 2x);
          background-image: image-set(url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_600,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="m" absolute="true"}}) 1x,
              url(https://res.cloudinary.com/<YOUR_USERNAME>/image/fetch/w_1000,c_fit,q_auto,f_auto,dpr_auto/{{img_url background size="l" absolute="true"}}) 2x);
      }
  }